The licensed sellers underwent a state and local licensing process that included public hearings to ask neighbors about shop locations. Owners also underwent more than a dozen fire and building inspections for each shop.

Recreational use of marijuana for adults 21 and over has been legal in Colorado for more than a year, but retail selling of the drug will not be legalized until 8am on Jan. 1.

Washington, the only other US state to allow recreational use of the drug by adults, plans to have stores open by late spring next year.

Denver is one of 19 municipalities and seven counties in Colorado that will allow retail sales of recreational marijuana.

Existing medical marijuana businesses are now allowed to make the transition to recreational sales.

Licensed shops were handed red posters and stacks of fliers on Friday explaining the limits of marijuana to customers, including the fact that users can not consume marijuana in public, drive under the influence of the drug or take marijuana out of the state.